Various types of WDM optical modules have been developed, and a WDM optical transceiver is one of them. For example, a WDM optical transceiver provided with a TOSA (Transmitter Optical Sub-Assembly) which multiplexes a plurality of optical signals emitted from a plurality of light sources and having different wavelengths has been developed. Japanese Patent Application Laid-Open Publication No. 2007-279507 (Patent Document 1) and Japanese Patent Application Laid-Open Publication No. 2008-203427 (Patent Document 2) describe an optical transceiver provided with a TOSA in which four semiconductor lasers (LD: Laser Diode) having different oscillation wavelengths are disposed in a row.